1. Technical Field
The present invention relates to a method for manufacturing a metal-oxide thin film transistor.
2. Description of Related Art
Metal-oxide thin film transistors (TFTs) are transistors utilizing metal oxide as semiconductor layers. As compared to amorphous silicon TFTs, metal-oxide TFTs possess high carrier mobility, and therefore exhibit excellent device characteristics. In addition, the method of manufacturing metal-oxide TFTs is simpler than that of low temperature polycrystalline silicon TFTs, so that metal-oxide TFTs are advantageous in having a better productivity.
In conventional methods of manufacturing metal-oxide TFTs, the device characteristics of metal-oxide TFTs are unstable when the metal-oxide semiconductor layers are not annealed. FIG. 1 is a graph showing relationships between the gate voltage and the drain current when the drain voltage is 20V, in which the same unannealed metal-oxide TFT is measured six times under identical conditions. As depicted in FIG. 1, each of the six measured results differs from the others, and the threshold voltage of the metal-oxide TFT shifts significantly. The variation of the threshold voltage is about 9.36V. In order to resolve this repeatability problem, an anneal process at a temperature of over 350° C. is unitized to improve the stability of the metal-oxide TFT. However, the metal-oxide TFT is deformed during the anneal process because of the thermal stress generated in the high-temperature anneal process.
In view of the above, there exists a need for a new method that would improve the stability of metal-oxide TFTs and lower the temperature of the anneal process.